Such a vane cell machine is known, for example, from US 2013/0108498 A1.
During a rotation of the rotor, the work chambers have to increase and to decrease their volumes. To this end, it is known to position the rotor eccentrically in a bore of the stator. The work chambers have the smallest volume in a region in which a distance between an axis of the rotor and the inside of the stator is smallest. In the above mentioned US 2013/0108498 A1 the ring is positioned centrically with respect to the bore of the stator and has an eccentric bore accommodating an axle of the rotor. The ring can serve as axial bearing for the rotor.
However, the use of an asymmetric ring, i.e. a ring with an eccentrical hole for the rotor, makes mounting of the machine complicated since the ring has to be mounted with an exact angular position within the side wall of the stator. The asymmetry also causes unwanted forces from pressure to act on the ring.